[30P.13] Clouds near Great Red Spot and White Oval. Spectral Classification and Interpretation of Galileo Images in 26 Wavelengths

We present maps of Jovian cloud properties derived from
images taken simultaneously by the Galileo Solid State
Imaging system (SSI) and the Near Infrared Mapping
Spectrometer (NIMS) at visible and near infrared
wavelengths, 0.41 to 5.2 microns. Regions containing the
Great Red Spot (GRS) and one of the White Ovals were
studied. The cloud properties are derived using a radiative
transfer model and principal component analysis (PCA) on the
image data. The mean spectrum for each region was subtracted
from individual spectra taken at each point and the
resulting deviations were studied using PCA. The deviation
spectra are highly correlated. For example, only three
spectral functions (principal components) are needed to
describe 92% of the variations. Our results suggest that
clouds inside GRS contain violet absorber while White Oval
do not have it, even though the regions are similar in other
wavelengths. We used a radiative transfer model to determine
what variations in the cloud structure correspond to the
principal components. Our model is based on the cloud
structure that accounts for the spectrum of GRS averaged
over the region derived in Banfield et al. (1998). Based on
the modeling, the first principal component indicates a
simultaneous increase in the optical depth and elevation of
the optically thick cloud near the NH3 condensation level
(approximately 0.6 bar) within both the GRS and White Oval.
The difference between principal components 2 and 1 is
interpreted as the variation in single scattering albedo of
the diffuse cloud layer occupying the 0.2 - 0.6 bar level.
The corresponding map suggests a narrow ring of dark haze
surrounding the GRS and White Oval at these altitudes.
Another possibility is that the difference PC2 - PC1
represents a variation in optical thickness of the cloud at
0.6 bar, but the fit is not as good.

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